Vises are usually employed in machine shops and the like for temporarily holding various sizes of workpieces in the desired position for drilling and the like. The adjustable jaw of the vise is usually moved forwardly toward and rearwardly away from the fixed jaw by rotating a handle connected to a screw shaft on which the adjustable jaw is supported. When unclamping the workpiece it is the usual practice to rotate the handle a greater distance than is actually required to provide sufficient clearance for removal of the workpiece so that a greater amount of rotation must be again applied to the handle when moving the adjustable jaw back into clamping position with a subsequent workpiece. There is usually some "play" between the external threads of the screw shaft and the internal threads of the adjustable jaw so that it is usually necessary to rotate the handle a greater distance than the amount required to move the adjustable jaw when both clamping and unclamping the workpiece. These problems are not significant except when repetitively clamping and unclamping a particular size of workpiece in the vise for repetitive drilling operations and the like.
It is generally known to adapt a vise to repetitive clamping and unclamping of a particular size of workpiece without requiring excessive rotation of the handle. For example, U.S. Pat. No. 1,279,011 discloses providing a separate handle supported in an eccentric manner between the adjustable jaw and the connection with the screw shaft so that rotation of the handle imparts limited forward and rearward movement to the adjustable jaw to provide a quick adjustment for clamping and unclamping workpieces of the same size. However, the addition of this handle is costly and requires extensive modification of a conventional type of vise. U.S. Pat. No. 2,818,786 discloses a vise equipped with a separate elbow lever mechanism for rapid and repetitive clamping and unclamping of workpieces. The elbow lever mechanism supported in a position to be rocked by an eccentric carried by a manually movable handle to move a portion of the elbow lever into and out of clamping engagement with the workpiece. The adoption of this type of clamping and unclamping device is also costly and requires substantial modification of a conventional type of vise.